1. Field of the Invention
This invention relates to an apparatus for manually sharpening the blades of cutting tools, in particular, knives or scissors.
2. Description of Related Art
Various forms of apparatuses having two sharpening elements allowing both sides of a blade to be processed, and thereby sharpened, simultaneously, are already known.
For instance, the patents DE 202 03 955 U1 and U.S. Pat. No. 4,599,919 provide for a sharpening apparatus in which two crossed sharpening elements (plates of hard metal) form a V-shaped gap for sharpening. The processing angle formed by the V-shaped gap in these cases is permanently predetermined. The hard-metal plates in DE 202 03 955 U1 have a basic rectangular shape, whereas in U.S. Pat. No. 4,599,919 the basic shape of the sharpening elements includes a triangular tip at one end. In both of these documents the two sharpening elements of the apparatus have the same shape as one another, each with two sharpening edges. This configuration makes it possible to exchange the sharpening elements for one another so as to employ the other sharpening edge of each of them, which increases the working life if the sharpening elements.
A disadvantageous feature of these constructions, however, is that the sharpening process always occurs at the same place on whichever sharpening edges are operative, so that this site rapidly becomes worn down. According to DE 202 03 955 U1, all that can be done is to make a second edge site usable by rotating the sharpening elements through 180° and exchanging their positions.
It is known from U.S. Pat. Nos. 562,223, 584,933 and 6,393,946 B1 to dispose the sharpening elements so that they can be rotated about an axis and fixed in selected positions within the sharpening apparatus. By appropriate choice or adjustment of the rotational position of the sharpening elements, the sharpening edges can be set at the desired angle for processing the blades. In this arrangement, a different site on the sharpening edges is used for sharpening, depending on the selected angle. For a given angle, however, it is always the same edge site that is used, and since in practice such an apparatus is often used repeatedly for blades of the same kind, rapid wear results. To prolong the working life, these documents disclose only that each of the sharpening elements comprises several sharpening edges, which can be employed in succession by appropriate repositioning of the cutting element.
The patent GB 505,871 furthermore, discloses a sharpening apparatus in which the operative site on each sharpening edge depends on the pressure with which the knife to be sharpened presses against the edge, and on the opposing force generated when the user presses the parts of a handle together. Here it is disadvantageous that the relative position of the two sharpening elements cannot be fixed, so that the effective sharpening region varies continuously and is determined only at random.
Accordingly, a sharpening apparatus which overcomes these disadvantages, is desired.